As someone mentioned above, studies have demostrated a 'halo' effect where looks are concerned. From an evolutionary point of view, human beings have always correlated positive, non aesthetic, traits with appearance - the phenotype is a quick way to determine genetic superiority, and mating suitability. As such, those who are considering good looking are also deemed to be, predominantly on a subconscious level, more capable in other respects - whetehr that be in terms of intelligence, compassion, sociability etc.
Of course, on a more conscious level, bias can depend upon the employer, the industry and those conducting interviews/the hiring process. Certain industries/employers which require the applicant to be client facing or to espouse a brand image, i.e. fashion, good looking candidates will be favoured.
Ultimately, I would suggest that, with the exception of certain industries and employers, this effect is secondary to qualifications/job suitability. It is also largely irrelevant, unless one is considering modelling, as, besides the basics of adherence to a basic grasp of style, grooming and self-care, very little can be done about one's appearance. I would add, however, that I recently read an article on PsychologyToday which cited a study suggesting that these factors - style, self-care, grooming, confidence etc. - have a far greater effect on the projected image of an individual than natural good looks.